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Old 26th Feb 2021, 8:51 pm   #1
Valvewhiz1
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Default Marconi Generator Help

Hi all,
More lockdown fun, Iíve just dug out a long dormant Signal Generator No. 18 Mk2 CT402 Marconi /TF995A/3/S.
Partially working except for the 54 to 108MHz band and the 108 to 220MHz band.

The question is does anyone have manual / circuit diagram for this, I have the standard TF995A/5 but this one has a different circuit and an add on IF amplifier and supply panel TM5347.

Regards
Amanda M0DZO
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Old 26th Feb 2021, 10:40 pm   #2
Julesomega
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Default Re: Marconi Generator Help

I have the front panel and a few remains of a TF995A/2 if you are looking for any bits. 0n the sub-assemly for the modulator and crystal calibrator there are big differences from the schematic shown on Radiomuseum - I'm hanging on to the crystal unit and I'd like to know what's inside it.
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Old 26th Feb 2021, 11:12 pm   #3
Julesomega
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Default Re: Marconi Generator Help

Nice coincidence that you asked as I currently have this on the floor awaiting assessment and recovery of most of the bits. Haven't yet got round to opening up the calibrator osc unit, but have been wondering why it needs 3 wires going into it when it already uses the chassis gnd
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Old 26th Feb 2021, 11:29 pm   #4
Terry_VK5TM
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Default Re: Marconi Generator Help

This will take some digging around on the internet - the US Air Force have these listed as amongst equipment they used to have - plant number 6625 6340 5103.

There is/was a site or public access portal that carried a lot of the US forces service manuals, but I can't find it at the moment, hopefully someone else will remember it.
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Old 27th Feb 2021, 10:50 am   #5
geeoboeh2s
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Default Re: Marconi Generator Help

Have you looked at the Marconi Instruments group on .io. There are ex-Marconi people on there.

Chris
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Old 27th Feb 2021, 11:06 am   #6
geeoboeh2s
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Default Re: Marconi Generator Help

Sorry, I should have provided a link.

https://groups.io/g/Marconi-Test-Instruments

Chris
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Old 27th Feb 2021, 5:14 pm   #7
Valvewhiz1
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Default Re: Marconi Generator Help

Hi all,
Thanks for the info so far, Iíve joined the Marconi group, with perseverance the top two bands are working now, most of the valvebases in the rf stage had a brown goo on them, cleaned this off which helped a lot, then looked at the underside of the rf chassis, sticky brown goo around the valve pins of the vhf frequency stages which appears to be resin flux.

I will report further on it as I progress.

Regards
Amanda M0DZO
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Old 27th Feb 2021, 7:22 pm   #8
vintage_8bit
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Default Re: Marconi Generator Help

I have a 995B/2 this also has flux all over, all of the valve bases. I have also changed numerous high value resistors in mine.

Colin
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Old 28th Feb 2021, 10:48 am   #9
David Simpson
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Default Re: Marconi Generator Help

Amanda, there is also the massive VMARS online military archive. Well worth a visit.
If the inside of the 995's cabinet smells a bit like old fly spray, then the "brown goo" might well be the pan-climatic fungicide which many items of military test equipment were sprayed with internally. Some brylcreme boy, pongo or matelot might have been a bit heavy with a spray can back in the 60's.
As I have an A/5 & an A/2, like many other Marconi enthusiasts, will find your thread excellent reading.

Regards, David
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